Arthrocentesis (removing fluid from a joint) can help health care providers look for joint problems. It also can help treat too much fluid in a joint.

A joint is where two bones meet in the body (for instance, the elbows, knees, shoulders, hips, and wrists). The area inside the joint contains a liquid called synovial fluid. This fluid cushions the bones and helps them move easily.

When a joint is swollen or painful, taking a sample of synovial fluid can help a health care provider find the cause of the problem. To get the synovial fluid sample, your child's health care provider carefully inserted a needle into the joint. The health care provider may have used ultrasound to help see inside the joint and guide the needle to the right place. Before putting the needle in, the health care provider may have numbed the skin and/or given your child medicine to relax or sleep through the procedure. After taking the sample, the health care provider put a bandage on the joint.

The health care provider will share the test results with you when they come back from the lab.

• If your child had medicine to relax or sleep during the procedure, he or she may need to rest for a few hours afterward.
• Follow your health care provider's instructions for giving any prescribed medication.
• Follow the health care provider's instructions for when to take off the bandage.
• If your child has pain, give acetaminophen or ibuprofen.
• Your child may shower or bathe as usual.
• Your child should do any range-of-motion exercises recommended by the health care provider.
• Follow the health care provider's instructions about when your child should return to regular activities. This is usually within 48 hours.

• If your health care provider told you to make follow-up appointments, call to schedule them.

Your child has:

• Redness or swelling around the joint.
• A fever above 100.4°F (38.0°C).
• More than a small amount of drainage or bleeding from the injection site.
• Increased pain or pain that does not improve within 2 days.
• Pain that is not relieved by acetaminophen.

Your child has:

• Severe pain.
• Difficulty moving the joint.